I think if you were able to see a breakdown of the twitter population, you would see it's used by business owners on one hand, and people with lots of free time on the other.

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In prosperous, secure societies, most people do indeed have plenty of free time. Some use it to tell their friends what they ate/who they dated/what they are listening to/where they are at/the political assassination they just witnessed. Others may use it to talk drums on a specialty discussion board. Whether that is a waste of time is entirely up to the person taking the time.